This invention relates to the measurement of electrical radiation from a transmitting source, particularly in the RF bands. More particularly, the invention relates to a modular instrument wherein a sensitive meter movement contained in an electrical power measuring and indicating device (such as an RF insertion-type watt-meter) is used in combination with a removable field strength sensing module to indicate the level of the electrical radiation detected by the instrument.
Instruments for indicating the strength or intensity of electrical radiation from a transmitting source, especially in the RF bands, are generally self-contained devices with a sensing antenna, an amplifier, and an indicating component such as an LED, an audible alarm, or a relatively low-sensitivity type meter movement. Typical devices of this type are shown in the following U.S. patents:
U.S. Pat. No. 3,636,641 PA1 U.S. Pat. No. 3,908,165 PA1 U.S. Pat. No. 4,072,899 PA1 U.S. Pat. No. 4,186,351 PA1 U.S. Pat. No. 4,199,716.
Because of the relative nature and therefore restricted usefulness of such an instrument, a high quality, high sensitivity meter movement is generally not used because of its cost. A high sensitivity meter movement in such an instrument would, however, be of decided value in certain applications owing to the increased overall sensitivity that it could provide.
Other electrical measuring instruments that do utilize high quality, high sensitivity type meter movements are usually used for different purposes, such as power measurement. One type of instrument widely used in the RF field is an insertion-type wattmeter for measuring the level of the forward and/or reflected wave on a coaxial transmission line. For example, an RF directional wattmeter currently available is manufactured and sold by Bird Electronic Corporation, of Solon, Ohio, under the trade designation "Model 43." This instrument is adapted to be connected in or inserted in an RF tranmission line, and has its own integral coaxial line section. The line section has an elongated, tubular, conductive metal body with a central, cylindrical opening and a coaxial center conductor positioned therein. The metal body also has a transverse opening communicating with the central cylindrical opening and adapted to receive an inductive pickup coil contained in an interchangeable module removably mounted for rotation in the opening, about an axis normal to the axis of the line section. The pick-up coil is responsive to the voltage wave signal on the transmission line. The pick-up coil transmits a voltage signal to a D'Arsonval meter movement so that the meter provides an indication of the level of either the forward voltage wave signal or the reflected voltage wave signal, depending upon the orientation of the inductive pick-up coil.
The device of the present invention affords a unique means for utilizing a high-cost, high-sensitivity type D'Arsonval meter movement adapted for use in power measurement. More specifically, the device is an interchangeable module for the purpose of measuring and indicating the relative value of an electrical field intensity at a given point, resulting from waves radiated from a transmitting source. Thus, the modular instrument of the present invention affords features and advantages heretofore not obtainable.